1. Field of the Invention
The present invention relates generally to fabrics used in papermaking, and relates more specifically to fabrics employed in making corrugated board. The invention also relates to a belt for a corrugated board machine, where the belt includes a coating including an anti-friction modifier which can provide one or more of the following advantages: easy application of the coating to the appropriate area of the fabric, the coating is cost effective, the coating provides for increased belt life on the machine, and increased production quality of corrugated board. The present invention also relates to corrugated board machine including a belt which has a coating containing an anti-friction modifier. The present invention also relates to a method of making a coating for a belt, and a method of applying the coating to a belt where the coating includes an anti-friction modifier.
2. Discussion of Background Information
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation. It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Contemporary fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven or other type base fabric. Additionally, as in the case of fabrics used in the press section, the press fabrics have one or more base fabrics into which has been needled a batt of fine, nonwoven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the woven base fabrics may be laminated by placing at least one base fabric within the endless loop formed by another, and by needling a staple fiber batt through these base fabrics to join them to one another as in the case of press fabrics. One or more of these woven base fabrics may be of the on-machine-seamable type. This is now a well known laminated press fabric with a multiple base support structure.
In any event, the fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross.
Reference is now made more specifically to industrial fabrics used in the manufacture of corrugated paper board, or box board, on corrugator machines. Such an industrial fabric is used to form corrugator belts. On corrugator machines, corrugator belts support and pull a sheet of liner board and a sheet of paper board which pass over a roll which adds flutes or CD corrugations to the paperboard sheet. Then these at least two paperboard sheets supported by one or more belts are passed first through a heating zone, where an adhesive used to bond the at least two layers of the board together is dried and cured, and then through a cooling zone. Frictional forces between the corrugator belt, specifically the face, or board, side thereof, and the corrugated paper board are primarily responsible for pulling the latter through the machine.
Corrugator belts should be strong and durable, and should have good dimensional stability under the conditions of tension and high temperature encountered on the machine. The belts must also be comparatively flexible in the longitudinal, or machine, direction, while having sufficient rigidity in the cross-machine direction to enable them to be guided around their endless paths. Traditionally, it has also been desirable for the belts to have porosities sufficient to permit vapor to pass freely therethrough, while being sufficiently incompatible with moisture to avoid the adsorption of condensed vapor which might rewet the surfaces of the corrugated paper product.
As implied in the preceding paragraph, a corrugator belt takes the form of an endless loop when installed on a corrugator machine. In such form, the corrugator belt has a face, or boardside, which is the outside of the endless loop, and a backside, which is the inside of the endless loop. Frictional forces between the backside and the drive rolls of the corrugator machine move the corrugator belt, while frictional forces between the faceside and the sheet of corrugated board pull the sheet through the machine.
Corrugator belts are generally flat-woven, multi-layered fabrics, each of which is woven to size or trimmed in the lengthwise and widthwise directions to a length and width appropriate for the corrugator machine on which it is to be installed. The ends of the fabrics are provided with seaming means, so that they may be joined to one another with a pin, pintle, or cable when the corrugator belt is being installed on a corrugator machine.
In a typical corrugator machine, the heating zone comprises a series of hot plates across which the sheet of corrugated board is pulled by the corrugator belt. A plurality of weighted rollers within the endless loop formed by the corrugator belt press the corrugator belt toward the hot plates, so that the corrugator belt may pull the sheet across the hot plates under a selected amount of pressure. The weighted rollers ensure that the sheet will be firmly pressed against the hot plates, and that frictional forces between the corrugator belt and the sheet will be sufficiently large to enable the belt to pull the sheet.
However, corrugator belts currently available typically show preferential wear in the vicinity of the edges. This wear makes the belts unacceptable to manufacture a sheet of corrugated board of even quality across the boards width. In addition, because of wear in the vicinity of the edges of the corrugator belts, service life of the corrugator belts is greatly reduced.
In an attempt to solve premature wear problems associated with corrugator belts, U.S. Pat. No. 5,785,621 to BIRZELE, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses adding more wear resistant and/or more temperature resistant warp threads adjacent to the longitudinal edge of the belt. BIRZELE, however, utilizes the more wear resistant and/or more temperature resistant warp threads such that provides a belt which is complicated and expensive to manufacture.
U.S. Pat. Pub. No. 2004/0126544 to JAGLOWSKI, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses a fabric coated only on the high spots with a silicone material. JAGLOWSKI, however, utilizes the silicone material across the entire width of the fabric, which may allow migration of the coating material to the inside of the product, modifying its compressibility, and could result in running irregularities. Furthermore, the silicone material applied to the fabric in JAGLOWSKI increases the coefficient of friction of the corrugator fabric. That is, the increased coefficient of friction can lead to increased wear of the fabric.
U.S. Pat. No. 6,276,420 to LANTHIER, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses the use of a coated fabric to resist wear and more effectively allow corrugated board to pass through the machine. LANTHIER, however, utilizes the coating across substantially the whole width of the board. That is, the coating may affect the fabric runnability and productivity.